Caster

ABSTRACT

A conventional endless belt is made of a comparatively flexible member such as rubber. When the endless belt comes in contact with a gap, part of the belt is pushed inward against the gap to be depressed and as a result, a greater power is needed for the endless belt to climb over the gap and it becomes easily jamed. According to the present invention, a caster of an endless structure is provided which is almost jam-proof even in the case of a bigger gap.  
     The caster comprises a first wheel  3  supported on a mounting leg  2 , a second wheel  4  supported by an axle  8  on one end of a suspension arm  7  of which the other end is supported by an axle  6  which also supports the first wheel  3 , and a wrap-around member  5  which is wrapped around the first and second wheels  3  and  4 . The wraparound member  5  is formed an endless belt form by connecting independent pieces  25  to each other. The outer peripheral section of each piece  25  is provided with a wider section and when the wraparound member is depressed and warps, the wider section is adapted to touch a wider section of the adjacent piece  25 , thereby preventing further depression.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a caster for use in a wheelchair,furniture, vehicle, and the like which is almost jam-proof and capableof easily climbing over a gap or obstacle.

2. Description of the Prior Art

A caster for a wheelchair etc. comprising a pair of front and rearwheels and an endless belt wrapped around the wheels and designed to becapable of easily passing over a gap is known (for example, refer toPatent Document 1). A caster designed to climb stairs by tracked wheelsis also known (for example, refer to Patent Document 2).

Patent Document 1: Japanese Unexamined Patent Publication No. Hei8-225001

Patent Document 2: Japanese Unexamined Patent Publication No. 2002-3747(see FIG. 8)

When a caster with an endless belt climbs over a gap, the endless beltis pushed against the gap and depressed inward (i.e., toward the centerof a space surrounded by the endless belt or a wrap-around member in thesurface of rotation of the endless belt or the wrap-around member;hereinafter referred to as “inward”). The more the endless belt isdepressed, the greater the power needed to pass the gap. Accordingly, inthe Patent Document 1, many presser rollers are arranged inside theendless belt to prevent the belt from being depressed. However,arrangements of many rollers make a structure for holding these rollerscomplicated and the entire device large, increasing the weight, andthereby driving up costs.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to solve theseproblems.

To solve these problems, a caster according to claim 1 is provided withfirst and second wheels disposed forward and back and a wrap-aroundmember wrapped around the first and second wheels, and is characterizedin that the wrap-around member consists of a plurality of piecescontinuous in the circumferential direction. Each piece is provided withan outer peripheral section and an inner peripheral section which aremoveable independent of the adjacent pieces, permit the wrap-aroundmember to bend (hereinafter referred to as “inner bending” or “outerbending”) along the first and second wheels, and the outer peripheralsection is adapted to contact outer peripheral sections of the adjacentpieces when the wrap-around member is pushed inside the surface ofrotation by an external force, thereby preventing the wrap-around memberfrom being depressed inside the surface of rotation.

In claim 2, the caster according to claim 1 is provided, in which theouter peripheral section is provided in such a manner that the outerperipheral sections of the adjacent pieces contact each other when theyare close on a common tangent of the first and second wheels.

In claim 3, the caster according to claim 1 is provided, in which eachpiece is independently formed and connected to the others by aconnecting member in a circular form.

In claim 4, the caster according to claim 1 is provided, in which thepiece is provided with a tire section on the outer peripheral side and awheel guide section into which the outer peripheral sections of thefirst and second wheels are fitted.

In claim 5, the caster according to claim 4 is provided, in which thetire section and the wheel guide section are respectively formed asseparate bodies.

In claim 6, the caster according to claim 1 is provided, in which thefirst and second wheels overlap each other when viewed from thedirection perpendicular to the surface of rotation.

In claim 7, the caster according to claim 1 is provided, in which thefirst and second wheels have different diameters and a plurality ofwheels with a larger diameter is provided in the direction of the axisof rotation.

In claim 8, the caster according to claim 1 is provided, in which thewrap-around member is provided with a tire section on the outerperipheral side and a wheel guide section on the inner peripheral side,the tire section is formed of a continuous endless belt, and the wheelguide section is provided to engage each outer peripheral section of thefirst and second wheels and is combined with the tire section to formthe piece.

In claim 9, the caster according to claim 1 is provided, in which thewrap-around member is provided with a tire section on the outerperipheral side and a wheel guide section on the inner peripheral side,the wheel guide section being provided to engage each outer peripheralsection of the first and second wheel sections and formed of acontinuous endless belt, and the piece is formed by the tire section andthe wheel guide section.

In claim 10, the caster according to claim 1 is provided, in which thewrap-around member is formed of a single endless belt in its entiretyand slits cut in from the outer peripheral side at the same interval inthe longitudinal direction and grooves, wider than each slit, formedfrom the inner peripheral side at the same interval in the longitudinaldirection form the piece.

In claim 11, the caster according to claim 1 is provided, in which thefirst wheel is provided in such a manner that the diameter is ⅕ or lessof that of the second wheel and its thickness is substantially the sameas that of the second wheel, wherein the first wheel is disposed closeto the outer periphery of the second wheel so that the first and secondwheels are disposed on the same straight line when viewed from thedirection of each thickness.

In claim 12, the caster according to claim 11 is provided, in which aplurality of first wheels is provided along the outer periphery of thesecond wheel.

In claim 13, the caster according to claim 1 is provided, in which eachpiece is provided with a protrusion on one side of the piece in thefront and rear direction and a depression on the other side thereof,wherein the protrusion of one piece is inserted into the depression ofthe other piece which is adjacent forward and back, thereby connecting awall section surrounding the depression to the protrusion by a singleshaft.

In claim 14, the caster according to claim 1 is provided, in which ajoint piece provided with pipe sections on either end of each piece inthe front and rear direction is provided and each pipe section is fittedinto each depression formed on the pieces which are adjacent forward andback, thereby connecting each piece to the pipe sections by a singleconnecting shaft.

In claim 15, the caster according to claim 1 is provided, in which aconnecting plate having a pair of connecting holes is provided, eachconnecting hole being caused to correspond to a through-hole formed onthe central section of the adjacent piece in the front and reardirection, and a connecting shaft is inserted into these connectingholes and through-hole, whereby each piece can be connected by such asingle connecting shaft.

According to claim 1, a wrap-around member is formed by a plurality ofpieces that are connected to each other and continue in thecircumferential direction. Each piece is provided with an outerperipheral section and an inner peripheral section that are moveableindependent of the adjacent pieces to permit the wrap-around member tobend inward. When the wrap-around member runs over a gap, thewrap-around member is pushed against the gap from outside, depressedinward and the front and rear sections are bent outward. However, theadjacent outer peripheral sections mutually contact each other in thecircumferential direction to prevent the depression from beinggenerated. In this manner, the wrap-around member is not depressed, butis substantially straight while running over the gap. Thus, thisstraight section functions as an anti-sticking plate to permit thewrap-around member to climb over the gap, thereby improving the gapclimbing performance.

This depression preventing function can be realized by the structure ofthe wrap-around member itself and no separate presser rollers and platesare needed inside the wrap-around member. In this manner, these pressermembers can be made useless and there is no necessity to support thesemembers. As a result, it is possible to provide a simple structure, makethe entire device compact and lightweight, and reduce costs.

According to claim 2, in a section of the wrap-around member close on acommon tangent of the first and second wheels, the outer peripheralsections of the adjacent pieces mutually contact to exhibit a depressionpreventing function. In this manner, it is possible to maintain astraight condition, as-is, in the section of the wrap-around memberclose on the common tangent which is normally straight.

According to claim 3, since each piece is formed independently, it ispossible to easily form the wrap-around member by coupling theseindependent pieces together by a suitable connecting member in a ringshape. It is also possible to exchange part of the wrap-around member oradjust the length thereof.

According to claim 4, since the piece is provided with a tire sectionand a wheel guide section, the tire section can provide satisfactoryground contact performance, while the wheel guide section can preventdisengagement of a large diameter wheel from a small diameter wheel toprovide good transmission of rotation.

According to claim 5, since the tire section and the wheel guide sectionare respectively formed as separate bodies, combination of the tiresection with the wheel guide section can be selected such as exchange ofthe tire section in accordance with the intended use and as a result, itis possible to freely change the performance.

According to claim 6, since the first and second wheels are provided tooverlap each other in a side view, it is possible to make the entiredevice compact.

According to claim 7, since the first and second wheels are provided tohave different diameters and a plurality of wheels with a largerdiameter is provided in the direction of the axis of rotation, it ispossible to consolidate the wheel on the larger diameter side that is aload-carrying main body.

According to claim 8, the wrap-around member is provided with a tiresection on the outer peripheral side and a wheel guide section on theinner peripheral side, the tire section being formed of a continuousendless belt, and the wheel guide section being connected to the tiresection to form the piece. In this manner, it is possible to assemblethe wrap-around member only by mounting each wheel guide section on thecommon tire section formed in the endless belt shape and thus make theproduction easy.

According to claim 9, the wrap-around member is provided with a tiresection on the outer peripheral side and a wheel guide section on theinner peripheral side, the wheel guide section is formed of a continuousendless belt, and the piece is formed by the tire section and the wheelguide section. In this manner, it is possible to assemble thewrap-around member only by mounting each tire section on the commonwheel guide section formed of the continuous endless belt and thus makethe production easy.

According to claim 10, the wrap-around member is formed by a singlemember in its entirety, the peripheral section being formed by a slitcut in from the outer peripheral side, and the inner peripheral sectionbeing formed by a groove, wider than the slit on the outer peripheralside, formed from the inner peripheral side. In this manner, it ispossible to reduce the number of parts, realize the simplest structure,and thus make the production easy.

According to claim 11, a first wheel of a minimum size is provided. Eventhough the first wheel is provided on the same line on the outerperipheral section of a second wheel, it is possible to arrange thefirst and second wheels without increasing the center distance. In thismanner, the first wheel can be provided in the same width as the secondwheel even in the axial direction. It is therefore possible not only tomake the caster compact in its entirety, but also to increase anapproach angle and improve the gap climbing performance.

According to claim 12, the first wheel of the minimum size is provided.A plurality of first wheels can be disposed along the outer periphery ofthe second wheel. In this manner, it is possible to make the castercompact and reduce each allotted load.

According to claim 13, since the piece is provided with a protrusion anda depression, it is possible to couple the adjacent pieces together by asingle connecting shaft.

According to claim 14, since a joint piece provided with pipes isprovided, it is possible to couple the adjacent pieces and joint piecetogether by a single connecting shaft. It is also possible make thestructure of the piece simple.

According to claim 15, since connecting holes of the adjacent connectingplates and a through-hole of the piece can be overlapped to be connectedby a connecting shaft, it is possible to unite the connecting shaftsinto one and simplify the structure of the piece.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a caster according to a first embodiment of thepresent invention;

FIG. 2 is a view showing the situation when the caster according to thefirst embodiment climbs over a gap;

FIG. 3 is a cross-sectional view taken along line 3-3 of FIG. 2;

FIG. 4 is a schematic view showing a wrap-around member according to thefirst embodiment;

FIG. 5 is an enlarged view of part of the wrap-around member;

FIG. 6 is a cross-sectional view taken along line 6-6 of FIG. 5;

FIG. 7 is a view showing the assembly of the wrap-around member;

FIG. 8 is a view showing part of the wrap-around member in the inwardbent condition;

FIG. 9 is a view showing a line of the wrap-around member in a commontangent section;

FIG. 10 is a view similar to FIG. 1 according to a second embodiment;

FIG. 11 is a view showing a variation according to the secondembodiment;

FIG. 12 is a cross-sectional view of one piece in the circumferentialdirection according to a third embodiment;

FIG. 13 is a view showing the assembly of a wrap-around member accordingto the third embodiment;

FIG. 14 is a cross-sectional view of part of an outward inflexible areain the circumferential direction according to a fourth embodiment;

FIG. 15 is a cross-sectional view taken along line 15-15 of FIG. 14;

FIG. 16 is a view corresponding to FIG. 14 according to a fifthembodiment;

FIG. 17 is a view similar to FIG. 12 according to the fifth embodiment;

FIG. 18 is a cross-sectional view taken along line 18-18 of FIG. 17;

FIG. 19 is a view similar to FIG. 9 according to a sixth embodiment;

FIG. 20 is a cross-sectional view taken along line 20-20 of FIG. 19;

FIG. 21 is a cross-sectional view taken along line 21-21 of FIG. 19;

FIG. 22 is a view similar to FIG. 19 according to a seventh embodiment;

FIG. 23 is a view similar to FIG. 21 according to the seventhembodiment;

FIG. 24 is a view similar to FIG. 4 according to an eighth embodiment;

FIG. 25 is a view similar to FIG. 9 according to the eighth embodiment;

FIG. 26 is a view similar to FIG. 7 according to the eighth embodiment;

FIG. 27 is a view similar to FIG. 26 showing another example accordingto the eighth embodiment;

FIG. 28 is a view showing a bottom surface side of a tire section ofsaid another example according to the eighth embodiment;

FIG. 29 is a view similar to FIG. 26 showing still another exampleaccording to the eighth embodiment;

FIG. 30 is a cross-sectional view showing an engaging section of theexample of FIG. 29;

FIG. 31 is a view similar to FIG. 29 showing still further exampleaccording to the eighth embodiment;

FIG. 32 is a cross-sectional view showing an engaging section of saidexample of FIG. 31;

FIG. 33 is a perspective view showing part of a wraparound memberaccording to a ninth embodiment;

FIG. 34 is a cross-sectional view taken along line 34-34 of FIG. 33;

FIG. 35 is a view showing an inward bending condition according to theninth embodiment;

FIG. 36 is a view similar to FIG. 34 according to a tenth embodiment;

FIG. 37 is a cross-sectional view taken along line 37-37 of FIG. 36;

FIG. 38 is a view showing the assembly according to the tenthembodiment;

FIG. 39 is a plan view of a fixed section according to an eleventhembodiment;

FIG. 40 is a front view of the fixed section according to the eleventhembodiment;

FIG. 41 is a left side view of the fixed section according to theeleventh embodiment;

FIG. 42 is a right side view of the fixed section according to theeleventh embodiment;

FIG. 43 is a side view of a caster according to a twelfth embodiment;

FIG. 44 is a side view showing a substantial part of a driving sectionaccording to the twelfth embodiment;

FIG. 45 is a view schematically showing the arrangement of the casteraccording to the twelfth embodiment;

FIG. 46 is a side view of a caster according to a thirteenth embodiment;

FIG. 47 is a perspective view of a piece according to a fourteenthembodiment;

FIG. 48 is a longitudinal sectional view of the piece according to thefourteenth embodiment;

FIG. 49 is a view showing the connecting condition of pieces accordingto a fifteenth embodiment;

FIG. 50 is a view showing the assembly of the piece according to thefifteenth embodiment;

FIG. 51 is a perspective view of a joint piece according to thefifteenth embodiment;

FIG. 52 is a cross-sectional view taken along line 52-52 of FIG. 49;

FIG. 53 is a cross-sectional view taken along line 53-53 of FIG. 52;

FIG. 54 is a perspective view showing a variation of the joint piece;

FIG. 55 is a perspective view showing another variation of the jointpiece;

FIG. 56 is a view showing the connecting condition of pieces accordingto a sixteenth embodiment;

FIG. 57 is a cross-sectional view taken along line 57-57 of FIG. 56; and

FIG. 58 is a cross-sectional view taken along line 58-58 of FIG. 57.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The above and other objects, features and advantages of the presentinvention will become more apparent from the following description whentaken in conjunction with the accompanying drawings

A first embodiment of a caster of the present invention will now bedescribed with reference to FIGS. 1 through 9. FIG. 1 is a side view ofa caster, FIG. 2 is a view showing the caster climbing over a gap, andFIG. 3 is a cross-sectional view taken along line 3-3 of FIG. 2. FIG. 4is a view showing a wrap-around member, FIG. 5 is an enlarged viewshowing one of pieces forming the wrap-around member, FIG. 6 is across-sectional view taken along line 6-6 of FIG. 5, FIG. 7 is a viewshowing the assembly of the wrap-around member, FIG. 8 is a view showingpart of the wraparound member in the bent condition, and FIG. 9 is aview showing part of the wrap-around member in the straight condition.

Referring first to FIGS. 1 and 2, a caster 1 comprises a mounting leg 2,a first wheel 3 of a small diameter supported by the mounting leg 2,second wheels 4 of a large diameter supported by the mounting leg 2, anda wrap-around member wrapped around the first and second wheels 3 and 4.

The first wheel 3 is rotatably supported by an axle 6 on the mountingleg 2 and the second wheels 4 are rotatably supported by an axle 8 onone end of a suspension arm 7 of which the other end is coaxiallysupported by the axle 6 on the mounting leg 2 together with the firstwheel 3.

The suspension arm 7 is a cantilevered member extending from themounting leg 2 in a substantially horizontal position. Provided betweenthe vicinity of the axle 6 of the suspension arm 7 and the mounting leg2 is a suspension spring 9 which is adapted to absorb the verticalmovement of the second wheels 4 due to the unevenness of the roadsurface. The suspension arm 7 can be a coil spring or various knownsprings made of metal, rubber or the like.

The first wheel 3 and the second wheels 4 are respectively made ofsuitable material such as metal or plastic and are provided to overlapin a side view as shown in the figures to make the caster 1 compact.

The caster 1 excels in performance when climbing over a gap 10 such asunevenness or stairs and can easily climb over even the gap 10 of whichthe height H is larger than the radius of the second wheels 4. This willbe described later.

The mounting leg 2 is attached to a member 13 to be attached to a devicesuch as a wheelchair by an upward projecting screw 12 through a joint11. The screw 12 and the mounting leg 2 are provided to rotate aroundthe axis line of the screw 12 by the joint 11. In other words, thecaster 1 is freely rotatable type with the suspension.

Reference numerals 14 a and 14 b indicate an adjuster nut and anadjuster bolt and serve as part of a known tension adjustment mechanism15 for optimizing the tension of the wraparound member 5 by adjustingthe position of the axle 8 (see FIG. 2).

As shown in FIG. 3, the mounting leg 2 is formed with a substantiallyinverted U-shaped cross-section and the axle 6 is provided to bridge thevertical sections of the U. Each end of the axle 6 is fixed by a capsection 6 a and a fixing means 6 b such as a nut so that it does notdrop out. The fixing means 6 b can be a split pin or the like.

The first wheel 3 is rotatably supported on the center of the axle 6 inthe longitudinal direction through a bearing 16 and positioned by theright and left washers 17 and 17 and the right and left collars 18 and18 mounted on the outside of the axle 6.

The bearing 16 can be selected from various types of bearings such as aball bearing, a needle bearing and a metal bearing. However, a collarcan be used for the bearing depending on the circumstances. In thiscase, the first wheel 3 is positioned on the collar using an E-shapedclip.

Rotatably supported on each end of the axle 6 through collars 19 and 19is one end of the suspension arm 7 of a substantially U-shape of whichthe right and left sides are integrally formed. The collars 19 and 19are provided to engage the outer periphery of the axle 6 between themounting leg 2 and the collar 18 and the suspension arm 7 is positionedon the axle 6 in the axial direction by a flange section of the collar18 and the E-shaped clip.

The second wheels 4 are provided as a pair to sandwich the first wheel 3and have a dual wheel structure which can withstand a large load. Thesupporting structure of the right and left second wheels 4 and 4 is thesame as that of the first wheel 3 and both wheels 4 and 4 are rotatablysupported on an axle 8 through bearings 21 and 21. The bearings 21 and21 are positioned by a central collar 22, right and left washers 23 and23, and right and left collars 24 and 24 and the axial direction of thebearings 21 and 21 is positioned and fixed between a cap section 8 a ofthe axle 8 on one side and a fixing means 8 b such as a nut on the otherside.

The wrap-around member 5 consists of many independent pieces 25 whichcan be connected continuously in the circumferential direction and isformed of a ring or belt in its entirety. “Independent pieces 25” meansthat each piece 25 is in such a condition as to be capable of making amovement different from the adjacent piece on the outer and innerperipheral sides of the wrap-around member 5. In this case, each piece25 can be an independent piece or part of an integral body.

The piece 25 is provided with a tire section 26 adapted to serve as aground contact section and a wheel guide section 27 for supporting thetire section 26. The wheel guide section 27 is a comparatively rigidmember made of plastic, metal or the like. As closely shown in FIGS. 5and 6, the wheel guide section 27 is integrally formed with a pair ofsidewalls 28 for supporting both sides of the tire section 26 and aconnecting section 29 for coupling them together to support the bottomsurface of the tire section 26.

The wheel guide section 27 is further provided with a pair of guidewalls 30 and 30 consisting of parts where the sidewalls 28 and 28 extendinward over the connecting section 29. Formed at certain intervalsbetween these guide walls 30 and 30 is a pair of ribs 31 and 31 whichintegrally project from the connecting section 29. A guide groove 32 ais formed between the pair of ribs 31 and 31 and the outer peripheralsection of the first wheel 3 is fitted into this groove 32 a.

Further, formed between the guide walls 30 facing each rib 31 is a guidegroove 32 b into which the outer peripheral section of the second wheel4 is fitted. The guide groove 32 b is formed in pairs on both sides ofthe guide groove 32 a and corresponds to the right and left secondwheels 4 and 4. These guide grooves mutually position the first andsecond wheels and the wraparound member 5.

A connecting hole 33 penetrating the wheel guide section 27 in thecircumferential direction of the mounting leg 2 within the thickness ofthe connecting section 29 continuing perpendicular to the direction ofthe axis of rotation of the wheel is provided. A connecting member 34made of a resinous cord such as Nylon and Kevlar or a metal wire such asa piano wire is inserted into the connecting hole 33. The number ofconnecting holes 33 is arbitrary. The connecting holes are formed onboth ends in the figure, but the number of holes can be selectively set,wherein even one, three or four holes are acceptable in accordance withthe intended use.

As shown in FIGS. 4 through 8, the wrap-around member 5 according to thepresent embodiment consists of many independent pieces 25 which arecontinuous in the circumferential direction and are connected by theconnecting member 34. The wrap-around member 5 is formed of a ring or abelt continuous in the circumferential direction. As shown in FIG. 4,the wrap-around member 5 is provided to bend along the outer peripheryof the first and second wheels 3 and 4. In other words, the wrap-aroundmember 5 can bend inward, but it becomes straight on the common tangentsC1 and C2. As described later, the part of the wrap-around member 5 inthe straight condition becomes an outward inflexible area A (see FIG. 4)where the inward depression D as shown by an imaginary (virtual) line isprevented.

The connecting member 34 is not limited to the linear member as statedabove, but can be selected from the various shapes. For example, asshown by an imaginary line in FIGS. 6 and 7, it can be a sheet belt 34 ain which a cloth such as Kevlar or a belt-shaped member made of adequatemetal is formed in a ring shape. If this sheet belt 34 a is put on theconnecting section 29 and coupled together by adhesive bonding etc.,then the tire section 26 is fitted between the connecting section 29 andthe side walls 28 for integration, each piece 25 can be connected in thering shape by the sheet belt 34 a. In this case, since the connectinghole 33 can be omitted, it is possible to make the connection of eachpiece 25 simple and fast.

As shown in FIGS. 5, 8 and 9, the guide wall 30 of the wheel guidesection 27 is provided in such a manner that both ends in thecircumferential direction are inclined toward the inner peripheral sideto approach each other, thereby forming an inclined surface section 35.The guide wall 30 is therefore provided on the inward tip side with atapered narrow section relative to the sidewall 28. On the other hand,the sidewall 28 of the guide wall 30 on the outer peripheral side has awide section having the same width as the maximum width of the guidewall 30. Further, the inclined surface sections 35 and 35 between theadjacent pieces 25 and 25 form a substantially inverted V-shaped grooveto permit the inward bending of the wrap-around member 5. Each rib 31also has the same shape as the guide wall 30.

Each end of the sidewall 28 in the circumferential direction is providedwith a contacting section 36 of a linear shape running parallel to eachother. As shown in FIG. 9, when the wrap-around member 5 is in astraight condition, this section is provided in such a manner that thefacing contacting sections 36 and 36 of the adjacent wheel guidesections 27 and 27 contact each other to close a gap to prevent thewraparound member 5 from further bending outwards to warp. In thismanner, this contacting section 36 serves as a warp preventingcontacting section and thus, the contacting sections 36 and 36 of thewheel guide section 27 on the right and left sides function in the samemanner.

The tire section 26 of a block shape made of comparatively soft materialsuch as rubber is fitted between the right and left sidewalls 28 and 28and the right and left sides and the bottom surface are integrated byadhesive bonding etc. The side surfaces 37 of the tire section 26 in thefront and rear direction (the circumferential direction of thewraparound member 5 is hereinafter referred to as “the front and reardirection”) are flat surfaces parallel to each other and serve as thewarp preventing contacting section in the same manner as the right andleft contacting sections 36 of the wheel guide section 27. The outerperipheral section 38 of the tire section 26 is chamfered on the rightand left sides of the outer peripheral section and serves as a sectionfor contacting the ground as the tire section for the caster 1.

As shown in FIG. 7, the piece 25 is made in such a manner that the wheelguide section 27 and the tire section 26 are respectively made inadvance as separate bodies and the tire section 26 is fitted between thesidewalls 28 of which the right and left sides are facing and thensecured on the inner surfaces of the sidewalls 28 and the cross section29 by adhesive bonding etc. In this case, the side surfaces 37 of thetire section 26 in the front and rear direction are flush with thecontacting sections 36 of the sidewalls 28 as shown in the side surfaceof the installation condition (see FIG. 7).

As shown in FIG. 8, in the case where the wrap-around member 5 bends onthe inner peripheral side, the adjacent pieces 25 can freely bendwithout causing interference with each other because the side surface ofthe guide wall 30 is provided with the inclined surface section 35.Reference numerals 39 a and 39 b in the figure are sweep holes foreliminating dirt or dust clogged between the adjacent pieces 25. Asshown by the reference numeral 39 a, one hole can be formed between theadjacent guide walls 30 and 30 or an independent hole like 39 b can beformed for each guide wall 30.

FIG. 9 shows a line of the piece 25 on the common tangent section andeach piece 25 is horizontally arranged in a substantially straightcondition on the common tangents C1 and C2 (see FIG. 4). In the strictsense, this line is formed in a very large radius. If the vertical endsof each piece 25, for example, the inner peripheral ends of the guidewall 30 are lined up along this radius, the contacting sections 36 and36 of each side wall 28 in the adjacent pieces 25 and 25 and the sidesurfaces 37 and 37 of each tire section 26 in the front and reardirection contact each other to prevent warping. Thus, this makes theinward bending of the wrap-around member 5 impossible as shown by animaginary (virtual) line in FIGS. 2 and 4, thereby preventing thedepression or outward bending.

In other words, the wrap-around member 5 only permits the substantiallystraight line condition in which the tire section 26 forming the outerperipheral section of each piece 25 and the sidewall 28 of the wheelguide section 27 as shown in FIG. 9 contact each other and the conditionin which the adjacent tire sections 26 and 26 and sidewalls 28 and 28 ofeach piece 25 open to permit the wrap-around member 5 to bend on theinner peripheral side in its entirety as shown in FIG. 8, thereby makingwarping, in which one part of the wraparound member 5 is depressedinwards and the other part in the front and rear relation bends on theouter peripheral side, impossible.

Since a section of the wrap-around member 5 corresponding to the lowercommon tangent section C2 is an area in which the outward bending isprevented even in the case of contacting the gap 10, this section isreferred to as an outward inflexible area A. This outward inflexiblearea A is formed of the large radius which forms part of an imaginarywheel W. This imaginary wheel W is an imaginary circle with an extremelylarge diameter having a radius common with the large radius that isalmost a straight line. In the case where the caster 1 passes the gap,this imaginary wheel W is regarded as the caster 1 and it is possible toconsider this a condition substantially the same as that the imaginarywheel W climbing over the gap 10.

The operation of this condition will now be described. FIG. 1 is anormal condition before passing the gap in which the mounting leg 2 ispushed up by means of the suspension spring 9, the axle 6 is provided ina higher position than the axle 8, and the outward inflexible area A ofthe wraparound member 5 corresponding to the common tangent sectioncontacts the gap 10. An approach angle α which is the angle at whichthis area contacts the gap is also a ground surface angle.

In this condition, if the caster 1 advances toward the gap 10, the sideof the axle 8 of the suspension arm 7 swings in the clockwise directionof FIG. 2 because the outward inflexible area A contacting the gap 10does not bend outwards. As a result, the second wheel 4 leaves theground against the suspension spring 9 and the caster 1 climbs over thegap 10 in this condition.

In this case, the outward inflexible area A changes position inaccordance with the swing of the suspension arm 7 and the approach angleβ is smaller (α>β). Accordingly, when the wheel weight w of the outwardinflexible area A contacting the gap 10 is converted to a horizontalforce F and a tangential force f, the horizontal force F serving as animpelling force becomes larger as the approach angle changes from α to ⊖and the common tangent C2 also changes position down. In this manner,the caster 1 can climb over the gap 10 with smaller power to provide agood climbing performance, thereby improving the gap climbingperformance.

This means that the caster 1 can lightly climb over the gap which becamerelatively small with less power because the area of the wraparoundmember 5 contacting the gap becomes a very large radius, the imaginarywheel W using the R as part of the outer diameter becomes extremelylarge, and the gap is traversed by such a huge imaginary wheel W. If thesuspension arm 7 swings as shown in FIG. 2, the imaginary wheel Wassumes in such a condition as to climb over the gap which is furtherlowered and as a result, the climbing performance improves further.

This gap climbing is possible until the height H of the gap 10 reachesthe higher limit position of the outward inflexible area A. In otherwords, the caster can climb over the gap up to a height close to theaxle 6 of the first wheel 3 and shows excellent climbing performancecompared to a conventional endless belt. Further, in the presentembodiment, the axle 6 is provided in a higher position than the axle 8and the first wheel 3 of a smaller diameter is provided to increase theground surface angle α of the common tangent C2 in the normal condition.In this manner, it is possible to increase an angle of attack againstthe gap 10 and make the gap climbing easy.

As described above, many independent pieces 25 are coupled together inthe circumferential direction to form the wrap-around member 5. Eachpiece 25 is provided with an outer peripheral section and an innerperipheral section adapted to be moveable independent of the adjacentpieces 25 by the tire section 26 and the wheel guide section 27.Provision of the outer peripheral section and the inner peripheralsection makes inward bending of the wrap-around member 5 possible andprevents the wrap-around member 5 from warping, thereby preventinggeneration of the partial depression D thereof when climbing over thegap. In this manner, since the common tangent section C2 of thewrap-around member 5 can maintain the substantially straight conditionwhen climbing the gap, it serves as an anti-sticking plate. With thisarrangement, the wrap-around member 5 can smoothly climb over the gap 10and the gap climbing performance improves.

Further, since this warp preventing function can be realized by thestructure of the wrap-around member 5 itself, there is no necessity toprovide separate presser rollers and presser plates inside thewrap-around member 5. In this manner, it is neither necessary to providethese presser members nor to support them. As a result, it is possibleto make the structure simple, make the caster compact in its entirety tosave weight, and reduce the costs.

Still further, in the area of the wrap-around member 5 close on thecommon tangents C1 and C2 of the first and second wheels, the outerperipheral sections of the adjacent pieces 25 contact each other toexhibit the warp preventing function. Accordingly, it is possible tomaintain the substantially straight condition as-is in the area close onthe common tangents C1 and C2 where there is normally a straightcondition. However, since the lower common tangent C2 affects the gapclimbing performance, the following description will be made onlyregarding the common tangent C2.

Since each piece 25 is independently formed, it is possible to easilyfabricate the wrap-around member 5 by coupling these pieces 25 togetherby a suitable connecting member 34 in a ring shape. It is also possibleto partially exchange the pieces 25 and adjust the length of thewrap-around member 5.

Since the piece 25 is provided with the tire section 26 and the wheelguide section 27, a good ground contact performance can be secured bythe tire section 26 and the disengagement of the first wheel 3 fromsecond wheel 4 can be prevented by the wheel guide section 27 to securesatisfactory transmission of rotation.

Further, since the tire section 26 is separately formed from the wheelguide section 27, it is possible to provide a free combination of thetire section 26 with the wheel guide section 27 such as the exchange ofthe tire section 26 in accordance with the intended use and thus freelychange the performance.

Since the first and second wheels 3 and 4 are provided to overlap in theside view, it is possible to make the caster compact in its entirety.Further, since the first and second wheels 3 and 4 have differentdiameters and a plurality of second wheels 4 of a larger diameter isprovided in the direction of the rotational axis, it is possible toconsolidate the second wheel 4 of the larger diameter which serves as amain body for supporting a load.

Further, since the second wheel 4 is provided with a suspensionmechanism, smooth gap mounting can be realized. Since the direction canalso be freely changed, it is possible to easily pass over the gap evenin this respect. Still further, since the direction can be freelychanged, running becomes easier.

A second embodiment will now be described hereunder. FIGS. 10 and 11 areside views of a caster of a simplified type without a suspension. In thecase of FIG. 10, a first wheel 3 is supported by an axle 6 at theintermediate section of a side surface 2 a of a mounting leg 2 with asubstantially C-shaped cross-section, while a second wheel 4 issupported by an axle 8 at the tip of the mounting leg 2 which extends tothe lower left. Other structures, the first wheel 3, the second wheel 4and the wraparound member 5 are the same as above or can be combinedwith various embodiments described below regarding the wrap-aroundmember 5.

In this manner, by omitting the suspension, the first and second wheels3 and 4 can be rigidly supported by a single mounting leg 2. Thus, it ispossible to reduce the number of parts and provide a simplifiedstructure. According to this type, an angle between the line drawn fromthe axle 6 to the axle 8 and a horizontal line is comparatively largeand the position of the axle 6 is considerably higher than that of theaxle 8. Accordingly, the caster of this type is suitable for use in ashopping cart for physically unimpaired people which requirescomparatively large power, but is capable of climbing over a large gap.

FIG. 11 also shows a rigid type caster, but in this case, the mountingleg 2 is made of a bent pipe member 2 b. The second wheel 4 is supportedby the axle 8 on the tip of a bent section 2 c of the pipe member 2 b,while the first wheel 3 is supported by the axle 6 on a bracket 2 dwhich projects backwards from the bent section 2 c. According to thistype, it is also possible to provide a further simplified structure. Inaddition, the axle 6 is situated close by and substantially at the samelevel as the axle 8 and an angle between the line from the axle 6 andthe axle 8 and the horizontal line is extremely small. Accordingly, thecaster of this type is suitable for use in a wheelchair for physicallyhandicapped or aged people which can climb over a gap of a certain sizewith the smallest possible amount of power.

In the case of either FIGS. 10 or 11, since the ground surface angle ofthe outward inflexible area A is constant, the angle is determined bysetting the mounting position of the axles 6 and 8 in advance. When theaxle 6 is lowered, the gap climbing performance improves because theapproach angle α becomes small. If the mounting position of the axle 6is set by manual adjustment or power assisted through a worm gear andthe like in the vertical direction and the like of the figure, theapproach angle can be more freely set. Mechanism for changing directioncan be freely selected for each type.

FIGS. 12 and 13 show a third embodiment. This and the followingembodiments relate to variations of the wrap-around member 5 in thestructure. These variations can be selectively combined for the caster 1of the types in various embodiments described above.

FIG. 12 shows a cross-section of one piece 25 in the circumferentialdirection and FIG. 13 shows its assembling method. A wheel guide section27 in this embodiment is integrally formed with a box-shaped securingsection 40. The box type securing section 40 opens upwards in the figureand the lower half side of the tire section 26 is fitted into thisopening section 41.

The side of the tire section 26 in the front and rear direction isformed with a step 37 a which is lowered into the box-shaped securingsection 40 according to the thickness. When combined, this step 37 a isfitted into the box-shaped securing section 40 and the lower end of anupper section 37 b is combined with the open end of the box-shapedsecuring section 40 so that the upper section 37 b is flush with thefront and rear sides 42 of the box-shaped securing section 40 (see FIG.12).

The other structures of the wheel guide section 27 on the side of guidegrooves 32 a, 32 b and 32 b are the same as those of the foregoingembodiments. In this manner, the tire section 26 can be positioned onlyby fitting it into the open section 41 of the box-shaped securingsection 40. Accordingly, it is possible to prevent the tire section 26from coming loose to maintain the outer diameter of the imaginary wheel.Also, since the front and rear sides 42 of the adjacent box-shapedsecuring sections 40 contact each other, it is further possible topositively maintain the outer diameter. It is also possible to makeassembling easy.

FIGS. 14 and 15 show a fourth embodiment. FIG. 14 is a cross-sectionalview of part of the wrap-around member 5 in an outward inflexible area Ain the circumferential direction and FIG. 15 is a cross-sectional viewtaken along line 15-15 of FIG. 14. The wheel guide section 27 accordingto the present embodiment corresponds to a structure in which thesection above the connecting section 29 of the wheel guide section ineach of the foregoing embodiments is omitted, wherein the lower surfaceof the tire section 26 of which the thickness in the height direction isreduced is combined with the upper surface of the connecting section 29,of which the thickness in the height direction is increased, by adhesivebonding and the like for integration. In this manner, it is possible toprovide the most simplified wheel guide section 27.

A fifth embodiment will now be described with reference to FIGS. 16through 18. FIG. 16 is a view corresponding to FIG. 14, FIG. 17 is across-sectional view of one piece 25 in the circumferential direction,and FIG. 18 is a cross-sectional view taken along line 18-18 of FIG. 17.In this example, the piece 15 is made of the same material such as hardrubber and metal in its entirety, wherein a wheel guide section isintegrally formed with a tire section. In this case, the outerperipheral side of the piece 25 is a tire section 26, the innerperipheral side thereof is a wheel guide section 27, and theintermediate section between them corresponds to a connecting section.An inclined section 35 and a contacting section 36, a connectingstructure using a connecting hole 33 and a connecting member 34, and awheel guide structure are the same as above. In this manner, it ispossible to provide the piece 25 with the most simplified structure.

FIGS. 19 through 21 relate to a sixth embodiment. FIG. 19 is a viewshowing a partial side of the outward inflexible area A, FIG. 20 is across-sectional view taken along line 20-20 of FIG. 19, and FIG. 21 is across-sectional view taken along line 21-21 of FIG. 19. In this example,each piece 25 is also made of the same material, but provided with, forexample, protrusions 43 protruding on the right and left sides. Theseprotrusions 43 are superimposed on depressions 45 formed on the rearsection of the side of the front and rear pieces 25 to allow an eyehole44 to correspond to a through-hole 46 on the side of the depression 45and coupled by an axle 47. In this case, an inclined section 35 havingan inclined surface provided in pairs in the foregoing embodiments isprovided only on one side and the other side is provided with asubstantially vertical notch section 35 a which serves as a clearancesection to avoid interference with the inclined section 35 of theadjacent piece 25 when bent inward.

In this manner, it is possible to assemble the wraparound member 5 byinterconnecting the adjacent pieces 25 as seen in the conventional metalchain and omit the connection by the ring shaped connecting member 34such as resin cord and metal wire as seen in each of the foregoingembodiments. It is to be noted that this connecting method can beapplied to each type of the foregoing embodiments in place of theconnecting member 34.

FIGS. 22 and 23 show a seventh embodiment having a similar connectingmethod to the above. FIG. 22 is a view corresponding to FIG. 19 and FIG.23 is a view corresponding to FIG. 21. In this example, a connectingplate 48 is provided to bridge the adjacent pieces 25 and is connectedby a connecting shaft 49 inserted into a through-hole 46. The upper endof the inclined section 35 is provided with a step 35 b which is cutinto the body section of the piece 25 to provide a wide groove whichserves as a clearance section between the facing inclined section 35 and35 to avoid interference with the inclined sections 35 of the adjacentpieces 25 when bent inwards. In this case, since the piece 25 can bemade in a symmetric figure including the front and rear direction,assembly can be made even though the pieces 25 are exchanged in thefront and rear direction. This example can also be applied to each typeof the foregoing embodiments.

FIGS. 24 through 32 relate to an eighth embodiment, in which a piece ismade separately from a tire section and composed of a wheel guidesection provided with sidewalls 28 which are coupled with the tiresection. The tire section is formed of an endless belt. FIG. 24 is aside view showing a wraparound member 5 in its entirety, FIG. 25 is viewshowing part of an outward inflexible area A, and FIG. 26 is a viewshowing an assembling method. In this example, the tire section isformed of the continuing endless belt 50. The endless belt 50 is made ofa suitable material such as rubber and each piece 25 is mounted in orderon the side of the endless belt in the longitudinal direction.

Each piece 25 is formed independently and for example, the structuresimilar to the wheel guide section 27 in the first embodiment can beused. As shown in FIG. 26, the sides 51 of the endless belt 50 in thewidth direction and the bottom surface 52 are inserted between thesidewalls 28 and secured to the inner surface of the sidewalls 28 andthe upper surface of a cross section 29 by means of adhesive bonding orthe like. In this case, the piece 25 is composed only of the wheel guidesection 27 which is made separate from the endless belt 50 and the outerperipheral section having a warp preventing function consists of thecross section 29 and the sidewalls 28 of the wheel guide section 27.

The inner peripheral section of the piece 25 consists of guide walls 30and ribs 31 of the wheel guide section 27. To facilitate bending of theouter peripheral section during inward bending, for example, the endlessbelt 50 can be formed of a laminated structure in which the materialbecomes softer on the outer peripheral side to make the elongation ofthe outer peripheral side easy. It is also possible to provide a slit onthe outer peripheral side.

Further, as shown in FIG. 27, the wheel guide section 27 with abox-shaped securing section 40 in the third embodiment can also be usedas the piece 25. The bottom surface side of the endless belt 50 is shownin FIG. 28. In this case, a bottom surface 52 is integrally formed atregular intervals in the longitudinal direction with a protrusion 53adapted to closely fit into an opening section 41. The protrusion 53 isfitted into the opening section 41 for integration. The structure of thepiece 25 in this case is the same as in FIGS. 25 and 26 and the outerperipheral section having the warp preventing function corresponds tothe box-shaped securing section 40 of the wheel guide section 27,wherein the front and rear sides 24 of the box-shaped securing section40 contact the front and rear sides 42 of the adjacent box-shapedsecuring section 40 in their entirety.

This arrangement makes positioning of the wheel guide section 27 easy.Since assembly can be realized only by mounting the wheel guide section27 on the common endless belt 50, assembly and production become easy.According to this example, in the outward inflexible area A, only thecontacting sections 36 (FIG. 26) or the front and rear sides 42 (FIG.27) of the adjacent wheel guide section 27 come into contact, but eventhese sections can fully prevent the outward bending of the wraparoundmember 5. As described in FIGS. 12 and 13, the warp preventing functioncan be positively exhibited if the wheel guide section 27 is providedwith the box-shaped securing section 40.

FIGS. 29 through 32 show that mounting of the wheel guide section 27 onthe endless belt 50 is done by engagement. Referring to FIGS. 29 and 30,the side surface 51 of the endless belt 50 in the width direction isformed with an engaging groove 54 which continues in the longitudinaldirection, while the end of the sidewall 28 of the wheel guide section27 is formed with a claw 55 which projects inwards. Thus, the claw 55engages the engaging groove 54 for integration. FIG. 29 shows anassembling method and FIG. 30 shows a cross-section of the engagingcondition.

FIGS. 31 and 32 show that the inner surface of sidewall 28 of the wheelguide section 27 is formed with an engaging protrusion 56 in place ofthe claw 55. FIG. 31 is a view corresponding to FIG. 29 and FIG. 32 is aview corresponding to FIG. 30. With this arrangement, it is possible tomount the wheel guide section 27 on the endless belt 50 through aone-touch operation.

In place of the engaging groove 54 which is an object to be engaged bythe claw 55 and the engaging protrusion 56, an engaging hole can beprovided on the side 51 of the endless belt 50 in the width direction ateven intervals in the longitudinal direction. Such an engaging structurecan also be applied to assembly of the tire section 26 with the wheelguide section 27 in the case where the piece 25 is independentlyprovided.

FIGS. 33 through 35 relate to a ninth embodiment in which a wraparoundmember 5 is formed of a continuing endless belt 60 in its entirety andeach piece 25 is integrally formed in one stretch. In this example, theouter peripheral section of the endless belt 60 serves as a tire section61 and the inner peripheral section thereof serves as a wheel guidesection 62. The wheel guide section 62 having wave-form irregularitiesin the side view is integrally formed with a guide groove 63 and a guidewall 64 in the width direction. Further, the side surface of the guidewall 64 of the wheel guide section 62 in the front and rear direction isprovided with an inclined section 65. A substantially triangular sectionin the side view is formed between the inclined sections 65 facingside-by-side, wherein each wheel guide section 62 is partitioned by thesection 66.

Further, the tire section 61 on the outer peripheral side is providedwith a slit 68 in the vertical direction toward a connecting section 67on the intermediate side. The slit 68 is formed at even intervals in thelongitudinal direction of the outer peripheral section of thewrap-around member 5. A section sandwiched by the adjacent slit 68 andsection 66 forms one piece 25 and each piece 25 is integrally andcontinuously formed with the others by the connecting section 67. Thewidth of the slit 68 is small and the sides facing on both ends of theslits 68 of each piece 25 contact the next to exhibit the warppreventing function. In this manner, the outward bending as shown inFIG. 34 is not permitted and the inward bending of the wrap-aroundmember 5 as shown in FIG. 35 is permitted.

In this manner, the wraparound member 5 can be formed in its entirety bya single member having many continuous pieces 25 and the outerperipheral section of the piece 25 is formed between the slits by theslits cut in from the outer peripheral side, and this section can permitthe warp prevention and inward bending of the wraparound member 5.Formed between the section 66 wider than the slit 68 on the outerperipheral side is the inner peripheral section of the piece 25 formedon the inner peripheral side which can permit the inward bending of thewraparound member 5. In this manner, it is possible to reduce the numberof parts forming the wraparound member 5, provide the simpleststructure, and make the production easy.

A tenth embodiment will now be described with reference to FIGS. 36through 38. In this embodiment, a wheel guide section 70 is formed of acontinuous belt and is provided with a guide wall 71 and an inclinedsection 72 at even intervals in the longitudinal direction. Formedbetween the inclined sections 72 facing side-by-side is a groove 72 awhich is substantially triangular in the side view. Each wheel guidesection 70 is divided by this groove 72 a. A guide groove 73 and a rib74 are integrally formed between the right and left guide walls 71 ofthe wheel guide section 70 in the width direction.

An upward projecting mounting block 76 is integrally formed on aconnecting section 75 of the wheel guide section 70 at even intervals inthe longitudinal direction. A tire block 77 is provided to cover themounting block 76. The tire block 77 is provided with a downward openingspace 78 formed on the thick section. The mounting block 76 is fittedinto and integrated with the downward opening space by means of adhesivebonding and the like.

The front and rear sides 79 of each tire block 77 are warp preventingsections which contact each other at the outward inflexible area A. Withthis arrangement, since the wheel guide section 70 can be formed with anendless belt shape, the wraparound member 5 can be assembled only bymounting each tire block 77 on the common wheel guide section 70. Thus,assembly and production of the wraparound member 5 become simple.

However, by reversing the fitting relationship of the tire block 77 tothe wheel guide section 70, a box-shaped structure similar to thesecuring section 40 shown in FIGS. 12 and 13 can be integrally formed onthe side of the wheel guide section 70 and the end of the tire block 77on the inner peripheral side can be fitted into the box-shapedstructure. In this case, the front and rear sides of the box-shapedstructure become the contacting sections to exhibit the warp preventingfunction.

An eleventh embodiment will be described with reference to FIGS. 39through 42. This embodiment shows variations of the third embodiment(see FIGS. 12 and 13). FIG. 39 is a plan view of a securing section,FIG. 40 is a front view, FIG. 41 is a left side view, and FIG. 42 is aright side view.

In these figures, a plurality of first protrusions 43 a is provided,each protrusion 43 a projecting from one surface of a connecting section29 at certain intervals and coaxially provided with through-holes 44 a(see FIG. 42). Second protrusions 43 b integrally projecting from theother surface of the connecting section 29 on the opposite side arefitted between the adjacent first protrusions 43 a and coaxiallyprovided with through-holes 44 b (see FIG. 41).

In the adjacent pieces 25, if the first protrusions 43 a and the secondprotrusions 43 b are alternately fitted between one another and thethrough-holes 44 a and 44 b are caused to correspond to be coupledtogether by connecting shafts 47, the first and second protrusions canbe coupled together. Even in this example, only one connecting shaft 47is necessary for one piece 25. Further, formed on the upper surface ofthe securing section 40 at certain intervals is a plurality of openings41 into which a mounting leg 37 a for a tire section 26 is fitted.

FIGS. 43 through 45 show a twelfth embodiment. The present andsubsequent embodiments are different from a caster of a dual wheel typein which a plurality of first wheels is arranged in the axial directionto sandwich the second wheel therebetween and relate to a caster of asingle wheel type in which a single wheel is arranged in the axialdirection. Accordingly, description will be made using differentreference numerals. In the present embodiment, a caster 100 having thesame wraparound member as in the first embodiment is provided, in whicha first wheel 103 is reduced in size to make the caster compact in itsentirety. FIG. 43 is a general view, FIG. 44 is a view showing only adriving section, and FIG. 45 is a view schematically showing thearrangement of each wheel.

In this example, a plurality of minimized first wheels 103 is arrangedin the vicinity of the outer periphery of a second wheel 104 andsupported by an axle 106 on a mounting leg 102. Each first wheel 103 isprovided to be moveable within a long hole 110 formed on the side of themounting leg 102 and the position thereof is simultaneously adjustableby a tension control member 111. The first wheel 103 has a diameter of ⅕or less, preferably of about 1/10 compared to that of the second wheel104.

As shown in FIG. 45, the width of the first wheel 103 in the thicknessdirection is almost the same as that of the second wheel 104 and eachwheel is collinearly disposed forward and back when viewed from thewidth direction. The number of the first wheels 103 is arbitrary and setto withstand the load required for the intended use. With thisarrangement, it is possible to make the width direction narrower becauseit is not necessary to provide a plurality of first wheels 103 atcertain intervals in the axial direction of the second wheel 104 tosandwich the second wheel 104 therebetween as shown in the example ofFIG. 3.

By making the first wheel 103 a minimum size, it is possible to providethe first wheel 103 in the vicinity of the outer periphery of the secondwheel 104, thereby reducing the center distance between the first wheel103 an the second wheel 104. Accordingly, even though the first wheel103 and the second wheel 104 are collinearly disposed, the caster 1 canbe made compact in its entirety.

Further, by making the first wheel 103 a minimum size, it is possible toimprove the gap climbing performance because the approach angle α can bemade larger. It is also possible to make the change of direction easybecause a ground contact section is one place as the characteristics ofthe caster and the ground contact width of the ground contact sectioncan be made narrower because of the above reason.

Reference numeral 108 is an axle for supporting the second wheel 104. Awraparound member 105 is wrapped around the first wheel 103 and thesecond wheel 104. The wraparound member 105 is almost the same as in theforegoing examples, but the number of wheel guide grooves formed on eachpiece is limited to one, as described later.

FIG. 46 shows a thirteenth embodiment. This embodiment is a variation ofthe previous embodiment (see FIGS. 43-45) in which a spring suspensionstructure is adopted. More specifically, one end of a suspension arm 107is swingably supported by an axle 107 a on a mounting arm 102 and theother end thereof is connected to a second wheel 104 by a suspensionspring 109.

The position of the axle 108 for supporting the second wheel 104 isadjustable by an adjustment mechanism 123 provided at the end of thesuspension arm 107. Tension of a wraparound member 105 can be adjustedby this adjustment mechanism 123. In this manner, impact from the otherside can be absorbed by the suspension.

FIGS. 47 and 48 show a fourteenth embodiment. This embodiment is avariation of the sixth embodiment (see FIGS. 19-21). FIG. 47 is aperspective view of a piece 125 and FIG. 48 is a cross-sectional viewthereof. In these figures, the piece 125 is provided in such a mannerthat a tire section 126 and a wheel guide section 127 are disposed aboveand below a connecting section 129 in the same manner as above.

Guide walls 130 of the wheel guide section 127 are made symmetric in thefront and rear direction (i.e., the right and left of the figure) andthe intermediate section of the wheel guide section 127 in the widthdirection is a single wheel guide groove 131 formed of a cut outdepression sandwiched between the right and left guide walls 130. Thiswheel guide groove 131 is provided for the piece 125 used in theexamples shown in FIGS. 47 and 48, wherein only one guide groove 131 isformed because only one first wheel 103 is used in the width direction(i.e., the direction of the axis of rotation). This applies to each ofthe following examples.

A protrusion 143 projecting from one side of the connecting section 129is formed to have the same width as the wheel guide groove 131 andadapted to fit between the guide walls 130 of the adjacent piece 125.The protrusion 143 is formed with a protrusion through-hole 144. Thewheel guide section 127 is provided with a depression 145 for receivinga protrusion 143 of the adjacent piece 125 which enters from theopposite side of the protrusion 143 of the connecting section 129. Thedepression 145 opens toward the wheel guide groove 131. The intermediatesection of the connecting section 129 in the front and rear direction isalso formed with a piece through-hole 146 passing through the depression145 in the width direction.

The protrusion 143 of one piece 125 is fitted into the wheel guidegroove 131 of the adjacent piece 125 and then inserted within thedepression 145. Since the protrusion through-hole 144 corresponds to thepiece through-hole 146 of the adjacent piece 125, a connecting shaft 149is inserted there for coupling. In this manner, the piece 125 can beconnected with a single connecting shaft 149. Further, a guide inclinedsurface 135 of the guide wall 130 can be symmetrically provided back andforth (i.e., the rotational direction of the wrap-around member isreferred to as “front”).

A fifteenth embodiment is shown in FIGS. 49 through 53. In thisembodiment, the adjacent pieces 125 are connected using a joint piece181 which is a separate body from the piece 125. FIG. 49 is a viewshowing the connecting condition of the piece 125, FIG. 50 is aperspective view showing a connecting method, and FIG. 51 is aperspective view of the joint piece 181. FIG. 52 is a cross-sectionalview taken along line 52-52 of FIG. 49 and FIG. 53 is a cross-sectionalview taken along line 53-53 of FIG. 52.

In these figures, the wheel guide section 127 of the piece 125 is formedof a substantially double housing provided with a wheel guide groove 131of a cut out depression formed between a pair of guide walls 130. Thejoint piece 181 is fitted within the wheel guide groove 131 and a firstpipe section 182 of the joint piece 181 is fitted into a second pipesection 183 of the adjacent joint piece 181, wherein the piece 125, andthe adjacent joint pieces 181 and 181 are coupled together by means of aconnecting shaft 149 inserted from the piece through-hole 146 formed onthe cross section 129. The end of the connecting shaft 149 is secured bya suitable means such as a screw 180. Caulking, circlip or the like arealso available as a simple securing method.

The joint piece 181 can be easily formed from a metal plate by pressmolding as shown in FIG. 51. The central section of one end of a platesection 184 is rolled in a pipe shape to form a first pipe section 182,while on the other side, a pair of second pipe sections 183 is formed ata certain gap 185 on each end of the plate section 184 in the widthdirection to sandwich the first pipe section 182 therebetween. Formedbetween the pair of second pipe sections 183 of the plate section 184 isa notch 186 for communicating with the gap 185 which rotatably supportthe first pipe section 182 of the other joint piece 181 fitted.

FIG. 54 shows a variation of the joint piece 181 in which the first pipesection 182 and the second pipe section 183 are integrally formed frommetal or resin material. With this formation, the joint piece can bemade simpler.

FIG. 55 shows another variation of the joint piece 181 in which manyfirst and second pipe sections 182 and 183 are formed and firstcomb-shaped and then formed from resin or metal. In this manner, sincethe fitting sections are increased, stable coupling can be maintainedeven for a large load.

A sixteenth embodiment is shown in FIGS. 56 through 58. This is avariation of the seventh embodiment (see FIGS. 22 and 23). FIG. 56 is aview showing the coupling condition and FIG. 57 is a cross-sectionalview taken along line 57-57 of FIG. 56. FIG. 58 is a cross-sectionalview taken along line 58-58 of FIG. 57.

In this example, connecting the piece 125 using a connecting plate 148is the same as above. However, a connecting hole 187 of one connectingplate 148 and a connecting hole 188 of the other connecting plate 148,of the adjacent connecting plates 148 in the front and rear direction,of a pair of connecting holes 187 and 188 formed on the connecting plate148, are superposed, then superposed on a single through-hole 146 formedon the center of the piece 125 in the front and rear direction, whereinthe pair of adjacent connecting plates 148 and 148 in the front and reardirection and the piece 125 are connected by a single connecting shaft149. In this manner, one each of through-hole 146 and connecting shaft149 need only to be provided for one piece 125.

It will be understood that the present invention is not limited to theembodiments described above, but may be varied in many ways. Forexample, if the contacting section 36 in FIG. 8 etc. is provided notonly to make the front and rear side thereof parallel, but also make itslightly open to the outer circumferential direction, it is possible tocontrol warping from the obtuse condition slightly before straightening.On the contrary, if the contacting section 36 is made to slightly taper,it is possible to prevent further warping in the slightly warpedcondition. In other words, the warp prevention in the present inventiondoes not always mean making part of the wraparound member 5 a straightcondition parallel to the common tangent C2, but it is possible tofreely adjust the extent of warping to be controlled within somepermissible range.

It is desirable that such a permissible range of warping be less than 5%of the length of the outward inflexible area A in which the amount ofdepression of the wrap-around member 5 can be regarded as the length ofthe common tangent section C2. This is a range of permissible bending ofthe wrap-around member 5 during climbing the gap. If such a range isset, it is possible to scarcely produce an effect of depression in gapclimbing. If the range is larger than 5%, the climbing performancedrastically deteriorates. The preferred permissible range is less than3% and if such a range is set, it is possible to maintain part of thewrap-around member 5 contacting the gap in a substantially straightcondition including the tolerance.

Further, the length of the outward inflexible area A varies with thecenter distance between the two axles 6 and 8, but if the centerdistance is set slightly larger than the radius of the second wheel 4adding the radius of the axle 6, the axle 6 is assumed to be innon-contact with the second wheel 4 and to approach the axle 8 whereverpossible. In this manner, since the length of the outward inflexiblearea A becomes shortest, it is possible to reduce a change of diameterdue to bending of the imaginary wheel W to as small as possible.

The present invention can also be applied for various purposes. It canbe used for almost all casters known in the market, for example, thefront wheels of a wheelchair, furniture such as a table, a wheeledstretcher, a shopping cart, and wheels such as a light car including ahandcart. Further, as shown by an imaginary (virtual) line in FIG. 1, ifa motor M is provided within the side surface of the second wheel, it isalso possible to provide a self-propelled device of a wheel motor type.

1. A caster having first and second wheels disposed forward and back andan endless wrap-around member wrapped around the first and secondwheels, characterized in that the wraparound member consists of aplurality of pieces continuous in the circumferential direction, eachpiece being provided with an outer peripheral section and an innerperipheral section which are moveable independent of the adjacent piecesand permit the wraparound member to bend along the first and secondwheels, and the outer peripheral section is adapted to contact the outerperipheral sections of the adjacent pieces when the wrap-around memberis pushed inside the surface of rotation by an external force, therebypreventing the wrap-around member from being depressed inside thesurface of rotation in excess of a predetermined amount.
 2. The casteraccording to claim 1, wherein when the outer peripheral section isprovided in such a manner that the outer peripheral sections of theadjacent pieces contact each other, when they are close on a commontangent of the first and second wheels.
 3. The caster according to claim1, wherein each piece is independently formed and connected to theothers by a connecting member in a circular shape.
 4. The casteraccording to claim 1, wherein the piece is provided with a tire sectionon the outer peripheral side and a wheel guide section into which theouter peripheral sections of the first and second wheels are fitted. 5.The caster according to claim 4, wherein the tire section and the wheelguide section are respectively formed as separate bodies.
 6. The casteraccording to claim 1, wherein the first and second wheels overlap eachother when viewed from the direction perpendicular to the surface ofrotation.
 7. The caster according to claim 1, wherein the first andsecond wheels have different diameters and a plurality of wheels with asmaller diameter is provided in the direction of the axis of rotation.8. The caster according to claim 1, wherein the wrap-around member isprovided with a tire section on the outer peripheral side and a wheelguide section on the inner peripheral side, the tire section is formedof a continuous endless belt, and the wheel guide section is provided toengage each outer peripheral section of the first and second wheels andis combined with the tire section to form the piece.
 9. The casteraccording to claim 1, wherein the wrap-around member is provided with atire section on the outer peripheral side and a wheel guide section onthe inner peripheral side, the wheel guide section being provided toengage each outer peripheral section of the first and second wheels andformed of a continuous endless belt, and the piece is formed by the tiresection and the wheel guide section.
 10. The caster according to claim1, wherein the wraparound member is formed of a single endless belt inits entirety and slits cut in from the outer peripheral side at the sameintervals in the longitudinal direction and grooves, wider than eachslit, formed from the inner peripheral side at the same intervals in thelongitudinal direction form the piece.
 11. The caster according to claim1, wherein the first wheel is provided in such a manner that thediameter is ⅕ or less of that of the second wheel and its thickness issubstantially the same as that of the second wheel, wherein the firstwheel is disposed close to the outer periphery of the second wheel sothat the first and second wheels are disposed on the same straight linewhen viewed from the direction of each thickness.
 12. The casteraccording to claim 11, wherein a plurality of first wheels is providedalong the outer periphery of the second wheel.
 13. The caster accordingto claim 1, wherein each piece is provided with a protrusion on one sideof the piece in the front and rear direction and a depression on theother side thereof, wherein the protrusion of one piece is inserted intoa depression of the other piece which is adjacent forward and back,thereby connecting a wall section surrounding the depression to theprotrusion by a single shaft.
 14. The caster according to claim 1,wherein a joint piece provided with pipe sections on either end of thepiece in the front and rear direction is provided and each pipe sectionis fitted into each depression formed on the pieces which are adjacentforward and back, thereby connecting each piece to the pipe sections bya single connecting shaft.
 15. The caster according to claim 1, whereina connecting plate having a pair of connecting holes is provided, eachconnecting hole being caused to correspond to a through-hole formed onthe central section of the adjacent piece in the front and reardirection, and a connecting shaft is inserted into these connectingholes and through-hole, whereby each piece is connected by such a singleconnecting shaft.